Many devices and calculation means for determining the time in different time zones of the world have been used in the past. However, all such prior means have required some form of calculation, or skilled operation, on the part of the user or a high degree of knowledge of, and familiarity with, the subject of world geography.
U.S. Pat. No. 594,410 to Margolis describes one such device comprising two overlapping maps which together rotate by means of the operation of a twenty-four-hour clock mechanism, one map being of the southern hemisphere and the other of the northern hemisphere. However, a high degree of visual confusion is caused by the use of such overlapping maps and it is difficult to identify the position of selected cities, or even countries, on such a combination of maps. Moreover, the Margolis patent does not provide a visual coding means whereby land areas falling within different time zones may be readily distinguished. The Margolis reference further does not readily lend itself to the marking of city and country names on the maps themselves because of the fact of there being two overlapping maps and, therefore, several areas having too many associated names to mark on the limited area provided.